It’s often observed that conservatives used to be very supportive of the individual mandate, and only came to see it as the greatest threat to American liberty in our country’s history because Obama employed the very same policy tool as one of the pillars of the Affordable Care Act.

Here’s some of the clearest proof yet, courtesy of Senator Jim DeMint. The South Carolina senator and Tea Party chieftain endorsed Mitt Romney in 2008. But a source close to DeMint, in what seems very much like an official leak, is now putting Romney on notice that there’s no way he’ll endorse the former Massachusetts Governor again unless he admits Romneycare — which also relies on the mandate — was a “colossal mistake”:

A source close to the conservative icon emphasized that, despite comments to The Hill indicating that Romney shouldn’t shoulder all the political blame for the Massachusetts healthcare plan, DeMint wouldn’t endorse Romney again unless Romney were to admit the plan was mistaken.

“It’s obvious Jim was just trying to be nice to the guy he backed over McCain, as many conservatives did in 2008,” said the source. “But he would never consider backing Romney again unless he admits that his Massachusetts health care plan was a colossal mistake.”

Reacting to this, Steve Benen points out that Romneycare was a well-known achievement when Romney ran for president last time. Steve asks: “If it was a `colossal mistake,’ why didn’t DeMint notice three years ago?”

It’s a good question. Indeed, it’s worth emphasizing again that when Romney ran the last time, his health reform achievement was considered proof of his qualifications for national office. But don’t take my word for it. Guess who else agreed at the time?

Jim DeMint, who cited Romneycare in a 2007 interview as — you guessed it — one of the key reasons he’d decided to endorse Romney:

DeMint, who spent most of his life in private business, admires Romney’s business background and believes Romney has shown the talent to apply that experience to government. “He has demonstrated, when he stepped into government in a very difficult state, that he could work in a difficult partisan environment, take some good conservative ideas, like private health insurance, and apply them to the need to have everyone insured,” DeMint says. “Those kind of ideas show an ability to bring people together that we haven’t seen in national politics for a while. We don’t need the nation to be more polarized.”

By the way, the claim by the source close to DeMint that Romneycare was a “colossal mistake” comes only two days after Gallup released new data showing that thanks in part to this “colossal mistake,” Massachusetts boasts the lowest percentage of uninsured of any state in the country.